Field of the Invention
The field of the invention relates generally to methods of producing eyewear lenses, particularly finished lenses and lens blanks using additive techniques rather than removal of excess material.
Description of Related Art
Prescription eyewear lenses are commonly used to correct human vision errors, aberrations and focusing deficiencies caused by genetics, age, disease or other factors. In addition to correcting physiological vision problems, eyewear lenses may be used as a fashion accessory or to protect the eyes from hazards or discomfort.
Prescription eyewear lenses must be prepared to meet each individual's specific vision requirements. Various techniques have been developed over the years to achieve this goal. One common technique involves stocking or obtaining semi-finished lens blanks that form a series of starting blocks with discrete surface curvatures such that only one side of the blank needs to be further shaped to achieve the given prescription. The surfaced lens then needs to be polished to an optical finish and edged to the eyewear frame shape individually selected. This can be a time-consuming process. More recently, another technique of digitally surfacing lenses using computer controlled machining has gained prominence. Digital surfacing often requires only a limited number of semi-finished lens blanks or other starting lens pieces, too, but the computer-controlled surfacing equipment allows more complex (e.g., multifocal) or individualized prescriptions to be prepared. This method can involve significant expenses in equipment and trained personnel.
Each of these techniques could be described as subtractive production methods, in which excess lens material is removed to create the desired prescription or lens properties. In such processes, there is often a significant amount of waste material that must be safely handled, stored and eliminated.
Another technique involves stocking or obtaining finished lenses that will only be edged to the individual's selected eyewear frame. This technique generates less waste material at the final edging facility. However, finished lenses typically only approximate prescriptions in 0.25 D increments of sphere and cylinder corrections and, therefore, may be less accurate for eyesight correction. Even if stocked at such 0.25 D increments, the number of stocked units needed to cover the wide range of prescriptions an eyecare professional will need is huge. Thus, either a very extensive inventory is required, or only a small range of prescriptions are stocked, usually those dispensed with the greatest frequency. These downfalls counteract the processing advantages that may be realized with finished lenses.
It would be desirable then, if alternative processes could be devised for eyewear lens preparation. Additive techniques may present another option. Some initial developments of additive-type techniques have been described in the prior art, but still require the use of at least one additional molding surface. For example, U.S. Pat. Nos. 4,873,029, 5,178,800 and 7,002,744 B2 each describe methods of producing various optical parts by positioning pre-existing lenses or forms at known, controlled distances from a molding surface to form a lens-forming cavity, placing liquid lens-forming material in the cavity, and solidifying the lens-forming material onto the pre-existing lens or form to form a new composite optical part when the molding surface is removed. However, these techniques still require at least one precision molding surface for manufacturing, and that molding surface must be prepared, properly stored and maintained to achieve consistent and acceptable optical-quality production.
Other additive techniques such as those based on stereolithography, fused deposition, ink jet or other 3-D printing advancements may be of interest. Many of these require a support on which to build the desired 3-dimensional part. Often these supports are flat platforms, which are not intrinsically suitable for prescription eyewear lenses. In addition, most supports are carefully removed or separated from the final printed object, acting only as a base upon which to build the desired object. Some developments have occurred for production of flexible contact lenses using these types of techniques. For instance, U.S. Pat. Nos. 7,905,594 B2, 8,240,849 B2, 8,313,828 B2, 8,318,055 B2 and EP 2265430 B1 describe use of a precision mold or a forming optic as the removable platform on which to build the contact lens. In these descriptions, the forming optic is a precisely shaped structure on which the 3-D part is built, and which is designed to impart its shape, by replication, to the 3-D part. Irradiating energy that causes the polymerization of the reactive solution is directed through the precision mold or forming optic to build the part against the mold or forming optic's precision optical surface. The ophthalmic part or contact lens is then removed from the mold or forming optic, to provide, by replication, an optical surface finish and desired lens curvature on the surface of the 3-D part that was in contact with the mold or forming optic. In another approach, U.S. Pat. No. 7,235,195 B2 describes contact lenses produced by stereolithography at the top of a liquid bath, specifically without the use of any mold or support. All features of the desired lens are created by spatially controlled polymerization of the surface of the liquid bath via radiation exposure, preferably from two beams at different angles.
However, some disadvantages of additive production hamper implementation of these techniques for eyewear lenses. Many of these techniques still require the use of at least one expensive and sensitive precision mold or forming optic (collectively, external shaping structures) in order to get the shape or surface finish desired on the created additive part. In addition, such external shaping structures must be robust enough to allow undamaged removal of the created part, and preferably, allow reuse for making multiple parts with the same precision external shaping structure. Other concerns with additive production include the cost, time and complexity of precision placement and control of material deposition, particularly for added layers. Eyewear lenses require much more material than contact lenses or intraocular implants and therefore exacerbate these disadvantages. In addition, materials suitable for additive production of general usage, non-optical plastic parts, or even materials suitable for small, thin, flexible contact lenses, may not combine the necessary optical and structural properties required for eyewear lenses that will be mounted in eyeglass frames. Yet, efforts toward improvements and new inventions in the field of additive production techniques are warranted given the potential advantages of these methods.